1. Field of the Invention
The present invention is related to a wireless transmission apparatus and a control system thereof, for transmitting information, which is input from a keyboard and other input means, to a personal computer and the like in order to operate the personal computer and the like from a remote place by manipulating the keyboard and the like.
2. Description of the Related Art
In general, an infrared remote controller, a wireless keyboard and the like employed in a wireless transmission apparatus have two different control functions. That is, as the normal control function, they output a make code indicative of a key depressing state and a break code indicative of a key releasing state. As another control function, in a low electric field in which a transmitted electromagnetic wave cannot be reached to a reception side, or in radio interference caused by other wireless apparatuses, they continuously transmit an all break code when all of keys are turned OFF, in order to avoid erroneous operation of an external control apparatus (personal computer and the like) provided on the reception side.
In this wireless transmission apparatus, an external remote control appliance connected to the reception side is controlled based on a key information which is once made on the reception side. Subsequently, a break code which is information to release the key depressed on the transmission side is output to the reception side. The reception side realizes a remote control operation by depressing a plurality of keys in amultiple mode, or a repeat process operation by continuously depressing a certain one key, by holding the key make information as a result of the key depression from the transmission side.
Considering that the key break code cannot be received when the radio interference occurs, in the control system of this wireless transmission apparatus, information that all of the keys are continuously brought into the break state is continuously transmitted to the reception side when all of the keys are not depressed. A system arrangement is known which previously prevents the erroneous operation of the remote reception apparatus due to the inferior transmission of the key break code when the radio interference occurs, utilizing the continuous transmission of the all break code. That is, even if the radio interference happens to occur, when it disappears, all of the key break.process operations are executed on the reception side to release the key make holding.
JP-A-9-204252 discloses a wireless keyboard apparatus capable of preventing the erroneous operation when the radio interference and the like happens to occur. The keyboard control unit of this conventional wireless keyboard apparatus is equipped with the function capable of continuously transmitting the all off code automatically when all of the keys are turned OFF, in addition to the normal operation for outputting a key ON code and a key OFF code. When the radio interference and the like disappear, the all off code is received by a receiver. Upon receipt of the all off code, the receiver transmits to a computer the key OFF code which turns a key in the ON state registered in a status register off, and deletes the number of the key in the ON state.
In the above-described prior art, the all off code is continuously transmitted when all of the keys are not depressed. As a result, even if the key is held is erroneously held in the key make state due to the worst environment and so forth including the radio interference on the reception side, when all of the keys are released at the time of the disappearance of the worst environment, the key which has been brought into the key make state on the reception side due to the radio interference can be always released only when the all off code (all off break code) is delivered to the reception side.
However, in the control system of the above-explained conventional wireless transmission apparatus, all of the keys are released and the all break code transmission process operation is required on the transmission side. Furthermore, the key make state cannot be solved unless this all break code signal is delivered to the reception side when the radio interference is solved even instantaneously. Then, the reception side cannot receive the all break code under such a condition that the occurrence of the radio interference is continued for a long term. Thus, the erroneous operation will occur due to the remaining key make state.
The present invention has been made to solve the above-explained problems, and therefore, has an object to provide a wireless transmission apparatus and a control system thereof which can completely preventing an erroneous operation of a remote reception apparatus due to an inferior transmission of a key brake code when a radio interference happens to occur, as follows. That is, even when the radio interference is continued for a long time period, a reception side can firmly sense the radio interference, and produces an all break code in order to release a remaining key make state of the reception side.
To achieve the above-described object, such a system is constructed in accordance with the present invention. That is, a transmission side continuously transmits a data packet containing identification data (or confirmation data) specifically given to a transmitter thereof in a certain time interval in a burst mode, whereas a reception side monitors the identification data transmitted from the transmission side in a link channel. In other words, a wireless transmission apparatus according to the present invention comprises: a transmission system including key input means, a wireless communication unit for transmitting an input key data code, and a transmitting antenna; and a reception system including a receiving antenna, a wireless communication unit, and reception key code analyzing means for analyzing a key make state and a key break state; wherein the transmission system regularly transmits an identification code to the reception system; and when the identification code is not detected regularly, the reception system automatically produces an all off code for informing an external appliance that all of keys are brought into a break state.
As previously explained, in the wireless transmission apparatus, by intermittently receiving the identification code plural times in a certain channel, the reception side can confirm that the reception channel is stable as a communication channel. Conversely, under a weak electric field condition where the strength of the electromagnetic wave is low, or under a radio interference condition where the transmission channel of the transmission side is forcibly changed and a wireless interference happens to occur, the reception side cannot detect the intermittently transmitting identification code. When the non-detection time is continued longer than a pre-selected time duration (a predetermined time), the reception side judges that data cannot be received from the presently communicated channel to self-judge that the link channel is unstable, so that it does not transmit information on the channel to the external appliance until the reception of the identification data is returned. Also, when the radio interference is determined, the reception side transmits the all key break code to control the external appliance so as to get out from the key make state. Therefore, such a system can be realized which can detect the radio interference of the reception channel due to the continuous reception or continuous non-reception of the identification code.
Then, if the number of the continuous reception OK or the number of the continuous reception NG due to the reception of a fixed-term identification code (ID code) is counted by the reception side system, as the remote control data packet is transmitted from the transmission side to the reception side between the transmission of the present identification code and the transmission of the next identification code, the reception system can easily judge as to whether or not the present data is data received while the electromagnetic wave condition is stable.
Also, by the reception count control process of the identification code, it is possible to judge that there is data which is transmitted between the present reception data and the next reception data but is not received in the reception system. If this judgement system is applied to a wireless transmission apparatus, the all key break code at the time of the radio interference can be produced only in the receiver.